The present invention relates generally to a device for causing a gas tight seal of a vessel containing gas to rupture, and more specifically to a device for venting gas from an airbag inflator.
1. Field of the Invention
Motor vehicles are provided with airbags to restrain the movement of vehicle occupants in a crash. Airbags are inflated with gasses that are generated by, stored in, or both generated by and stored in airbag inflators. Airbag inflators are often pressure vessels that are sealed with rupturable membranes that are caused to fail in a selected manner at a selected time to release gasses to the airbag. In some airbag inflators the rupturable seal may simply be burst open by pressure inside the inflator due to the gas pressure resulting from the generation of inflation gasses by burning gas generants inside the inflator housing or heating gasses stored in the inflator housing by burning a pyrotechnic material. However, some airbag inflators employ venting devices that cause a seal to fail in response to a signal from a control device and the present invention relates to an improved venting device of this category.
2. Discussion of the Prior Art
One manner of selectively causing a rupturable member to fail is to activate a small pyrotechnic device that generates hot gas and a shock wave to impact the rupturable member and blow an opening through the rupturable member. Examples of such venting devices are disclosed for example in U.S. Pat. No. 5,678,856 B1 and U.S. Pat. No. 6,062,599 B1.
The use of a projectile or piercing member to punch a hole in a rupturable member is disclosed for example in U.S. Pat. No. 3,806,153 B1 and U.S. Pat. No. 6,010,153 B1. The very precise tolerances required to make such venting devices work consistently can be very costly.
Because gas pressure in a pressure vessel like and airbag inflator can be very high, on the order of 1,400 kilogram per square centimeter (20,000 pounds per square inch) the rupturable member must be fairly robust making it difficult for smaller pyrotechnic devices to cause the rupturable members to fail in a consistent manner. Another limitation is the surface area of the rupturable member subjected to such high stresses is limited. Another manner of causing a rupturable member to fail is to support a surface of the rupturable member opposite the pressurized gas with a support or pillar, then remove the support provided or pillar allowing the gas pressure to cause the rupturable member to fail. Examples of such venting devices are disclosed for example in: DE 299 14 433 U1; GB 2 316 475 A; U.S. Pat. No. 3,788,596 B1; U.S. Pat. No. 4,203,616 B1; U.S. Pat. No. 4,289,327 B1; U.S. Pat. No. 5,603,525 B1; U.S. Pat. No. 6,206,420 B1; U.S. Pat. No. 6,217,065; U.S. Pat. No. 6,247,725 B1; U.S. Pat. No. 6,412,811 B1; and U.S. Pat. No. 6,830,264 B2.
Still other venting devices employ both a support and a pyrotechnic device to cause a rupturable seal to fail. U.S. Pat. No. 6,908,106 B2 and U.S. Pat. No. 7,131,663 B1 teach a device for opening a container storing the inflation fluid under pressure. The container has an outlet passage through which the inflation fluid flows from the container. A rupturable closure member is fixed to the container and blocks the flow of inflation fluid through the passage. A support for the rupturable closure member defines a chamber adjacent the rupturable closure member. The rupturable closure member has a first portion deformed into the chamber by the pressure of the inflation fluid and a second ring-shaped portion encircling the first portion. An igniter ruptures the closure member when actuated by shearing the first portion of the now ruptured closure member from the now opened second ring shaped portion. U.S. Pat. No. 6,908,106 B2 and U.S. Pat. No. 7,131,663 B1 teach that the support remains intact during the venting operation so the only way for gasses to exit the container is to pass around the exterior of the support which limits the cross sectional area of the passageway for the gas being vented. This is a problem when the function of a venting device is to vent gas from the container as rapidly as possible, for instance to restrict the force of a deploying airbag on an out-of-position or small vehicle occupant.
U.S. Pat. No. 6,029,995 B1 teaches a support structure in the shape of a cup with the base of the cup adjoining a rupturable closure member in a load bearing relationship so as to transmit a storage pressure force from the closure member to the inflator structure. Preferably, the cylindrical sidewall of the support cup has a plurality of axially extending score lines that are spaced apart circumferentially about its periphery. Each score line defines a coextensive stress riser that is rupturable under the influence of the combustion products emitted from an igniter. This facilitates rupturing of the support cup radially outward at the periphery of the cylindrical body. The fluid storage pressure acting outward against the end wall of the support cup also facilitates peripheral rupturing of the cylindrical body by blocking movement of the end wall into the chamber under the influence of the combustion products in the support cup. However, there is no teaching in U.S. Pat. No. 6,029,995 B1 that the end wall of the support cup does not remain intact and as such remains an obstacle to the evacuation of gasses from the pressure vessel.